A fiber optic overhead ground wire (briefly, OPGW) is an aerial cable suitable for being employed in electric power transmission or distribution lines. For example, OPGW cable can run between the tops of high-voltage pylons of an electric power transmission or distribution line, and performs two distinct functions at the same time: a grounding function (i.e., it connects the aerial line to earth ground for protecting the electric power transmission or distribution line against lightning strikes) and a telecommunications function (i.e., it supports transmission of data).
Construction of OPGW cable typically comprises an optical core containing optical fibers within an inner tube—generally made of stainless steel, aluminium or polymeric material—surrounded by one or more layer(s) of metal wires encircled, in turn, by an outer aluminium layer. The optical fibers perform the telecommunications function, and the metal layers perform the grounding function while protecting the optical core against mechanical stresses.
EP 0 092 980 discloses an overhead electric conductor. In particular, a flexible elongate body comprises a substantially circumferentially rigid and substantially circumferentially continuous central core of aluminium or an aluminium-based alloy having an elongate compartment within and extending throughout the length of the core; at least one optical fibre loosely housed in the elongate compartment; at least one layer of bare elongate elements of steel surrounding the central core; and at least one substantially circumferentially continuous outer layer of aluminium or an aluminium-based alloy surrounding the layer or layers of steel bare elongate elements, aluminium or aluminium-based alloy of the central core and/or of the outer layer at least partially filling interstices between the steel bare elongate elements. The circumferentially continuous outer layer of aluminium or an aluminium-based alloy is initially a single extrudate of substantially C-shaped transverse cross-section, one or each of the limbs of the C having been folded inwardly so that the gap between the free ends of the limbs is closed. Alternatively, the circumferentially continuous outer layer of aluminium or aluminium-based alloy may be a drawn-down tube.
U.S. Pat. No. 5,787,217 discloses groundwire cables for use with overhead power transmission lines. In particular, a unitary optical fiber core structure is surrounded by high tension metal or metal alloy strength members, preferably steel wires. Moving radially outward, in turn are encased within a metal or metal alloy tube which hermetically seals the fiber core structure and binds high tension wires. Tube may be, e.g. aluminum, in the case of terrestrial ground wire.
GB 2101505 discloses a method for manufacturing an optical fiber cable for submarine use. The optical fiber cable core comprises a plurality of optical fibers held together around a strength member to comprise an optical preform. The preform is arranged in an aluminium tube. A layer of high tensile steel wires are stranded helically over the tube, thereby forming a stranded strength member. An oversize aluminium tube is then directly extruded coaxially over the stranded strength member by a continuous extrusion process. The tube is subsequently drawn down and swung onto the stranded strength member so that the tube material fills at least the interstitial spaces between the wires and is in intimate contact with the layer of stranded wires.